Another important open debate concerns the comparison of clusters' and groups' metallicities in their outskirts (\(\sim R_{500}\)  and beyond). Whereas there is now striking evidence for clusters having their metallicity flattening with radius and converging toward an universal value of \(\sim \) 0.3 Solar [1]}, [2]}, [3]}, groups and elliptical galaxies have sometimes been measured with an uninterrupted decrease of metallicity down to at most 0.1–0.2 Solar [4]}, [5]}, [6]}, [7]}. The trend seems to be followed by the sample results of [8]}, [9]} and of [10]}. These results, however, should be interpreted with caution, given how recent atomic codes improvements changed our view on the Fe-L complex, its modelling at moderate resolution, and its associated abundance (Sect. REF ). Moreover, some past measurements may have been affected by the Fe-bias discussed above, as moderate exposures available per source did not necessarily allow to model outer regions with more than one temperature. We note, for instance, that the more recent sample measurements of [11]} and [12]} show hints of a flattening beyond \(\sim 0.3 R_{500}\)  that remains formally consistent with the 0.3 Solar value reported in clusters [2]}, [3]}. These results are in agreement with [15]}, who reported that the metallicity profile of the group UGC 03957 does not decrease further below 0.3 Solar, even at distances beyond \(R_{200}\) . Other measurements, on the other hand, show in-between results, with evidence of a flattening though around 0.2 Solar, i.e. below the universal value. This is the case for the galaxy group RX J1159+5531 [7]}, as well as (perhaps even more intriguingly) for the Virgo cluster [17]}.
